d2395fda44
Each target reads the theme from ?theme=dark|light on load and applies it to data-theme before first paint. A MutationObserver syncs theme changes back to the URL via replaceState, and a click handler appends ?theme= to cross-port navigation links automatically. The outer iframe shell (dev/index.html) uses postMessage to track theme changes from iframes and passes the param when switching tabs. For hiccup, the server also reads ?theme= and sets data-theme on the <html> element server-side to prevent any flash of wrong theme.